Vehicular power steering systems have developed from hydraulic systems to electro-hydraulic systems, and more recently, to the electric power steering systems currently in wide use. In the near future, steer-by-wire systems employing a highly advanced electronic control system may be put to practical use.
Electronically controlled steer-by-wire systems may be configured in such a way so as to eliminate the string column from existing electric power steering systems. In addition, a torque sensor and a steering angle sensor may be interconnected with a steering wheel so as to detect the steering intention of a driver. Accordingly, the torque sensor and angle sensor may be further configured to operate a separately installed actuator, such as a motor, thereby generating a steering force.
Because steer-by-wire systems as described above may no longer employ a steering column to achieve direct transmission of a string force, it may no longer be necessary to mechanically connect steering units provided at both wheels of the vehicle by means, for example, a link.
Due to the development of independent steer-by-wire systems wherein both steering units are provided at both vehicle's wheels and separated from each other, it may be possible to increase the available space within an engine compartment In order to achieve independent steer-by-wire systems, it is desirable to provide a steering actuator adapted to individually apply a steering force to the separate steering units provided at both vehicle's wheels. Preferably, the steering actuator further is small in si and light weight. In addition, the steering actuator should be capable of operation without a force transmitted from the vehicle's wheels. Moreover, the steering actuator must have accurate control for safety and the like.